Multipotent Neural Stem Cells (NSC) can be derived from adult and fetal central nervous system (CNS) tissue, embryonic stem cells (ESC), or iPSC and provide a partially committed cell population that has not exhibited evidence of tumorigenesis after long term CNS transplantation. Transplantation of NSC from these different sources has been shown by multiple investigators in different CNS injury and disease paradigms to promote recovery or ameliorate disease. Additionally, both Dr. Okano and Dr. Anderson’s groups have shown that human NSCs transplanted in the subacute period after spinal cord injury promote functional recovery. While the role of the host immune response has been considered in the context of immune-rejection, predominantly regarding the T-cell response, the consequence of an ongoing inflammatory response within the context of the tissue microenvironment for cell fate, migration, and integration/efficacy has been largely overlooked. Critically, the tumorigeneis, fate, migration, and integration/repair potential of a stem cell is driven by: 1) the intrinsic properties of cell programming, e.g., the type and source of cell / means used to derive the cell, and maintenance/differentiation of the cell in vitro; and 2) the extrinsic factors the cell encounters. Variations in the intrinsic properties of the cell may affect the potential of that cell for uncontrolled proliferation or the response of the cell to extrinsic factors that it later encounters, defining its fate, migration, and integration/repair potential. The Nakamura/Okano group has demonstrated that iPS-derived neurospheres (iPS-NS) exhibit a surprisingly large degree of variation in tumorigenesis potential after CNS transplantation, which is correlated with tissue source as well as differentiation and NS forming capacity. Moreover, the intrinsic properties of hNSC populations derived from different cell sources have not been broadly characterized; in fact, Dr. Okano’s group has published the first data in the field demonstrating the differences in fate and integration/repair potential between primary and secondary neurospheres generated via in vitro differentiation of mouse or human ESC and iPSC. In parallel, Dr. Anderson’s group has shown profound differences in the response of NSC derived from human fetal tissue versus hESC to extrinsic signals. Together, these data suggest that both characterization of the intrinsic properties of NSCs derived from different sources is essential for our understanding of the basic biology of these cells. Investigation of molecules and signaling pathways directing hNSC fate choices in the injured CNS microenvironment will yield new insight into the mechanisms of fate and migration decisions in these cell populations.
Progress has been excellent in the first year, as has communication between the groups.
The Nakamura/Okada/Okano laboratory has regularly shared and updated us on these important findings and the progress of Aim 1 at Keio University via emails, live phone conferences and face-to-face meetings. The latest meeting occurred at the International Stem Cell Meeting in Toronto (ISSCR, June 2011), where safety and efficacy data of the initial screenings of numerous hiPS cell lines are shared and discussed which will have a significant impact on which cell lines we will work with under Aims 2 and 3.
Additionally, the Anderson laboratory took the additional step of focusing on xeno-free cells for this grant, with the goal of advancing future knowledge of utility for clinical translation based on CIRM funding. Xeno-free cells are cells that are cultured under conditions in which they are not exposed to animal proteins. Towards this goal, we have successfully transitioned multiple ESC and iPSC lines to xeno-free conditions for both maintenance, and successfully differentiated these lines to a neural stem cell lineage under parallel conditions. Moreover, by taking this step we have significantly enhanced the comparability of different cell lines for intrinsic properties and extrinsic influences, enhancing the potential impact of this work in increasing our basic understanding of stem cell biology, and how to harness it. Finally, we have conducted the first of our experiments testing the role of cell intrinsic properties in defining responses to the in vitro and in vivo microenvironment. Our data suggest that there are clear differences in intrinsic properties between cell lines, consistent with our initial hypothesis.